This invention relates to preparing multi-layer articles having a fluoroplastic layer and an elastomer layer.
Fluorine-containing polymers (also known as xe2x80x9cfluoropolymersxe2x80x9d) are a commercially useful class of materials. Fluoropolymers include, for example, crosslinked fluoroelastomers and semi-crystalline or glassy fluoroplastics. Fluoroplastics are generally of high thermal stability and are particularly useful at high temperatures. They may also exhibit extreme toughness and flexibility at very low temperatures. Many of these fluoroplastics are almost totally insoluble in a wide variety of solvents and are generally chemically resistant. Some have extremely low dielectric loss and high dielectric strength, and may have unique non-adhesive and low friction properties. See, e.g., F. W. Billmeyer, Textbook of Polymer Science, 3d ed., pp. 398-403, John Wiley and Sons, New York (1984).
Fluoroelastomers, particularly the copolymers of vinylidene fluoride with other ethylenically unsaturated halogenated monomers such as hexafluoropropylene, have particular utility in high temperature applications such as seals, gaskets, and linings. See, e.g., R. A. Brullo, xe2x80x9cFluoroelastomer Rubber for Automotive Applications,xe2x80x9d Automotive Elastomer and Design, June 1985; xe2x80x9cFluoroelastomer Seal Up Automotive Future,xe2x80x9d Materials Engineering, October 1988; and W. M. Grootaert et al., xe2x80x9cFluorocarbon Elastomers,xe2x80x9d Kirk-Othmer, Encyclopedia of Chemical Technology, vol. 8, pp. 990-1005 (4th ed., John Wiley and Sons, 1993).
Multi-layer constructions containing a fluoropolymer enjoy wide industrial application. Such constructions find utility, for example, in fuel line hoses and related containers and hoses or gaskets in the chemical processing field. Increased concerns with evaporative fuel standards give rise to a need for fuel system components that have increased barrier properties to minimize the permeation of fuel or fuel vapors through automotive components such as fuel filler lines, fuel supply lines, fuel tanks, and other components of the engine""s fuel or vapor recovery systems. Various types of tubing have been proposed to address these concerns.
Adhesion between the layers of a multi-layered article may need to meet various performance standards depending on the use of the finished article. However, it is often difficult to establish high bond strengths when one of the layers is a fluoropolymer. Various methods have been proposed to address this problem. One approach is to use an adhesive layer or tie layer between the fluoropolymer layer and the second polymer layer. Surface treatments for the fluoropolymer layer, including solvent etching and corona discharge, have also been employed to enhance adhesion. In the case of fluoropolymers containing interpolymerized units derived from vinylidene fluoride, exposure of the fluoropolymer to a dehydrofluorinating agent such as a base has been used, as well as polyamine reagents applied to the fluoropolymer surface or incorporated within the fluoropolymer itself.
The invention relates to a method for enhancing the bond strength between a fluoroplastic layer and an elastomer layer of a multi-layer article. The elastomer may be a fluoroelastomer or a non-fluorinated elastomer. According to the method, a fluoroplastic composition that includes interpolymerized units derived from vinylidene fluoride (VDF) is applied to the surface of a precursor article that includes a curable elastomer layer, preferably by extrusion coating the composition in molten form through a crosshead die, to form a fluoroplastic layer. Preferably, the composition is applied directly to the surface of the elastomer layer. Prior to application of the fluoroplastic composition, the curable elastomer layer is thermally insulated to prevent it from undergoing substantial heating. In one embodiment, where molten fluoroplastic composition is extrusion coated through a crosshead die, thermal insulation is achieved by equipping the die with a sleeve located at least partially within the upstream end of the die that receives and thermally insulates the curable elastomer layer prior to application of the fluoroplastic composition.
Following application, the fluoroplastic layer is heated and the curable elastomer layer is cured (preferably thermally cured). Preferably, the elastomer cure occurs separately from and subsequent to heating of the fluoroplastic layer. The combination of thermally insulating the curable elastomer layer prior to application of the fluoroplastic composition and heating the fluoroplastic layer following application of the fluoroplastic composition results in formation of a strong bond between the fluoroplastic and elastomer layers upon cure, even in the absence of adhesion aids such as surface treatments, separate adhesive layers, and the like. For example, bond strengths of at least 15 N/cm, can be achieved.
Multi-layer articles prepared according to this method can be provided in a wide variety of shapes, including sheets, films, containers, hoses, tubes, and the like. The articles are especially useful wherever chemical resistance and/or barrier properties are necessary. Examples of specific uses for the articles include their use in rigid and flexible retroreflective sheets, adhesive articles such as adhesive tapes, paint replacement films, drag reduction films, fuel line and filler neck hoses, exhaust handling hoses, fuel tanks, and the like. The articles are also useful in chemical handling and processing applications, and as wire and cable coatings or jackets.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.